A Visual Encyclopedia of the Periodic Table

50

Alkaline Earth Metals

This ore contains just 0.7 g

(0.02 oz) of radium in every

1,000 kg (2,205 lb) of rock.

Forms

Radium

Ra

88

88 88 138

State: Solid

Discovery: 1898

Radium is the only radioactive member

of the alkaline earth metals. It is also the

rarest element in this group, and forms in small

amounts when the atoms of more common

metals – such as uranium and thorium – break

down. Radium atoms do not survive for long,

with most of them quickly decaying into

radon, a radioactive noble gas. This element

is highly dangerous and is rarely used today.

However, in the early 20th century, radium

compounds were in common use. Luminous

paints, like those used to make watch dials

In 100

years time,

only 4% of the

radium atoms in this

watch would have

broken down.

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050-051_Radium.indd 50 02/12/16 6:52 pm